The key is understanding that accounting is driving the policy. 'Unlimited PTO' really means 'uncounted PTO' because for most public companies in the U.S., once PTO is counted, the salary value of each vacation day becomes another liability which must be reported and carried on the balance sheet. It's no different from a payable debt like a bank loan, except the debt becomes immediately due in cash the moment the employee ceases employment for any reason (quits, retires, laid-off, fired). It's also a debt that cannot be delayed, negotiated or discharged even in bankruptcy.
In a competitive employment market, paid time off is just another part of the cash value of any compensation package. Employees compare the overall packages, so companies need to offer 'competitive' PTO. In the past decade, FAANG-ish valley companies have had to offer 4-6 (or more) weeks of PTO. I know people who took two weeks every year and 'banked' four weeks. They retired early after 12 years with an extra YEAR of cash salary paid in full the day they left. When 5-10% of a company's debt is owed to their own employees and could become immediately due at any moment - it can be a cash flow and accounting issue for companies.
By 'not counting' the PTO, any time off you don't take in the year you earn it doesn't go on the balance sheet as an unpaid debt from the prior year - meaning PTO becomes 'use it or lose it'. This isn't materially different than the EU where it's normal for most corporate employees always take every day of PTO anyway. In the U.S., where historical PTO trends were closer to 2-3 weeks and only recently grew to 4-6 weeks, the result was more employees took more PTO each year (which is net good), but one component of their overall comp package became a little less good because they could no longer 'bank' more than one year's PTO and cash it out. Earned PTO carry-over was capped at one year and any you didn't take disappeared, unless you made an agreement with your manager.
For example, I deferred a chunk of my vacation into the next calendar year because we were shipping a major product (I was happy to do so and suggested it myself as I was leading the product). Technically, I guess it wasn't 'counted' in any HR record-keeping so if I suddenly quit before I took the vacation, I might not have been paid for the extra two weeks I deferred from the prior year - but only if my boss and the company decided to be real jerks about it. Another reason not to work for jerks if you can avoid it. Also, it isn't smart for companies to not reasonably honor verbal agreements with employees because word gets around and no other employee would agree to defer any PTO and future big projects would suffer. This flexibility wasn't always only in the company's favor. There was also a time I deferred a week of PTO to the next year by verbal agreement which I lumped together with paternity leave when my kid was born. Note: I'm only familiar with the dynamics in the U.S. I believe they also apply in some other geos but regulations and financial reporting requirements differ per country.
I've spent a lot of time in the EU working with tech companies, have a lot of friends there in tech companies and am on the board of a Swiss company at the moment. While it's true the average corporate worker generally has more protected rights in the EU, in my experience that additional government regulation doesn't usually pay off in ways that really matter that much to most employees most of the time.
As a thought experiment, if offered a tech job in, say, downtown Zurich, how much extra money would be required for an avg EU tech worker to happily accept that same job under Bay Area employment law, protections and standards (at-will employment, non-banked PTO, etc) than under EU employment law, protections and standards? In other words, apples-to-apples what are those extra protections actually worth in cash value? I suspect the answer would be, at most, around $25K to $50K/year. But when you look at the total comp packages (salary, benefits, equity, 401k, etc) between Bay Area and Zurich tech workers, the delta is far greater than that. In effect, the bay area tech worker 'sold' that extra protection for a big chunk of cash and is using some of it to self-insure against the potentially increased volatility. I think a lot of EU tech workers would be delighted to make the same trade. Another way of looking at it is you've given up a lot of upside for a relatively small amount of guaranteed extra protection on the downside.
This might surprise you but the reality is, many of the potential employment abuses you may be concerned about are vanishingly unlikely to occur in practice. The point is, you can end up paying a lot for expensive 'tiger insurance' you probably won't ever use and don't really need. While you can feel good knowing you have extra protection from tigers, on a purely economic basis I averaged over $500k/yr over my multi-decade career in bay area tech. In good years, the equity could take it over a million. My own admin (with no college degree) averaged over $200k a year in total comp. The highest paid admin at the Zurich company I'm on the board of makes closer to 50k CHF (and living in downtown Zurich isn't much less than SF). So, the "US tech employment deal" may seem weird and perhaps less fair, but the extra half million dollars my admin earned over several years put a lot of 'social safety net' in the bank that she can spend whenever and however she wants - and she still works there for my old boss, still loves her job and has never had to use any protections or social safety net yet (she's probably over a million in extra total comp banked by now). In short, viewed objectively, it's a different deal but not necessarily a worse deal. In many cases, EU workers may be giving up far more value than they're actually receiving in return.
You assume that bay area technology jobs are the norm. They seem, as far as I can tell, to be the absolute anomaly in the U.S.
Tiger insurance seems very necessary for e. g. retail, restaurant, construction etc. workers in the U.S., as they seem to be disproportionally targeted by tigers and earn next to nothing.
Everyone deserves to be treated fairly, even if they don't live in California and know how to programm.
In a competitive employment market, paid time off is just another part of the cash value of any compensation package. Employees compare the overall packages, so companies need to offer 'competitive' PTO. In the past decade, FAANG-ish valley companies have had to offer 4-6 (or more) weeks of PTO. I know people who took two weeks every year and 'banked' four weeks. They retired early after 12 years with an extra YEAR of cash salary paid in full the day they left. When 5-10% of a company's debt is owed to their own employees and could become immediately due at any moment - it can be a cash flow and accounting issue for companies.
By 'not counting' the PTO, any time off you don't take in the year you earn it doesn't go on the balance sheet as an unpaid debt from the prior year - meaning PTO becomes 'use it or lose it'. This isn't materially different than the EU where it's normal for most corporate employees always take every day of PTO anyway. In the U.S., where historical PTO trends were closer to 2-3 weeks and only recently grew to 4-6 weeks, the result was more employees took more PTO each year (which is net good), but one component of their overall comp package became a little less good because they could no longer 'bank' more than one year's PTO and cash it out. Earned PTO carry-over was capped at one year and any you didn't take disappeared, unless you made an agreement with your manager.
For example, I deferred a chunk of my vacation into the next calendar year because we were shipping a major product (I was happy to do so and suggested it myself as I was leading the product). Technically, I guess it wasn't 'counted' in any HR record-keeping so if I suddenly quit before I took the vacation, I might not have been paid for the extra two weeks I deferred from the prior year - but only if my boss and the company decided to be real jerks about it. Another reason not to work for jerks if you can avoid it. Also, it isn't smart for companies to not reasonably honor verbal agreements with employees because word gets around and no other employee would agree to defer any PTO and future big projects would suffer. This flexibility wasn't always only in the company's favor. There was also a time I deferred a week of PTO to the next year by verbal agreement which I lumped together with paternity leave when my kid was born. Note: I'm only familiar with the dynamics in the U.S. I believe they also apply in some other geos but regulations and financial reporting requirements differ per country.